120 THEORETICAL AND GENERAL 



The activity of diosmosis is not necessarily increased by the existence 

 of streaming, but secondarily induced differences of osmotic pressure may 

 be perceptible between streaming and quiescent cells. 



Albuminous solutions containing 89 to 90 per cent, of water have 

 at 1 8 to 20 C. a viscosity of from 0-06 to 0-07 with 95 per cent, of water, 

 0-04 with 72 per cent., 0-29 C. G. S. units. 



Gravity exercises little or no influence upon streaming in small cells, 

 and only a very slight one on streaming in large ones. The velocity of 

 floating particles of greater or less density than the plasma may be 

 distinctly affected by gravity. This observation indicates that the 

 viscosity of the streaming plasma is comparatively low. 



As the temperature rises within certain limits the viscosity decreases, and 

 a large part of the increased velocity of streaming is due to this cause alone. 



To maintain velocities of 2 mm. and 0-4 mm. per minute in cells of 

 01 cm. and ooi cm. internal diameter, forces of approximately -875 and 

 2 1 -9 dynes respectively are required per gramme of moving liquid. The 

 amount of work done in a year represents a consumption of only ^ TnjVznjth 

 of a gramme of cane sugar per gramme of moving liquid in the first case, 

 and in the second represents only T Tmtftf tn of the energy of respiration, 

 even if 99 per cent, of the energy intended for streaming is wasted. Hence 

 the energy expended in streaming is a trifling fraction of that produced 

 by respiration. The force required increases enormously as the diameter 

 decreases, so that streaming or transference in mass of the highly viscous 

 ectoplasm through interprotoplasmic connexions becomes practically 

 impossible, although through the coarse pores of sieve-tubes a direct 

 transference of the watery contents is possible 1 . 



The direction of streaming is mainly determined by internal factors, 

 and in rotating cells a reversal is only possible in certain cases and under 

 very special conditions. Changes occur spontaneously, however, in cells 

 exhibiting circulation. 



The total resistance during circulation is greater than during rotation, 

 unless the velocity increases considerably, and hence a change from the 

 former to the latter after stimulation is not due to an increased energy of 

 streaming but to a change in the configuration of the protoplasm. 



The energy for streaming can be derived either from aerobic or 

 anaerobic metabolism. Certain species of Char a and Nitella are in fact 



1 According to de Bary (Comp. Anat., 1884, p. 177) finger-like processes from the proto- 

 plasmic contents of adjacent segments of a sieve-tube meet in the sieve-pores but remain distinct. 

 Flow in mass through the pores would involve the rupture of the limiting membrane, which would 

 need a considerable pressure owing to the small diameter of the pores. This discontinuity has, 

 however, only been observed in dead sieve-tubes. It probably results from the breaking of the 

 viscous protoplasmic threads at their thinnest points on death, which is a surface-tension effect 

 commonly produced in dying protoplasmic threads. 



